American dipper alongside mountain stream. Credit: Ohio State University
Posted: 28 Dec 2015 09:46 AM PST
A songbird species that flourishes on the salmon-rich side of dams in the western United States struggles when it tries to nest on the side closed off from the fish and the nutrients they leave behind. But the songbird and the rest of the divided ecosystem rebounds, faster than some experts expected, when dams come down and rivers are allowed to resume their natural flow….In one study, the researchers documented that American dippers with access to salmon were in better physical condition and more likely to attempt multiple broods of offspring in a season. They also produced larger female offspring and were more likely to stay in breeding territories year-round. The research, published early online, will appear in an upcoming issue of the journal Ecography….Tonra and his colleagues spent four years in Washington’s Olympic National Park and surrounding tribal, federal and private lands. The Elwha River winds through the park and is the site of the largest dam removal in history. Crews started tearing down the Elwha and Glines Canyon dams in 2011 and concluded in 2014, freeing the path for migratory fish for the first time in a century. Salmon, which do most of their growing in the ocean, carry marine-derived nitrogen and carbon back into freshwater systems when they return to spawn and die. They benefit animals and plants, whether through direct consumption or because nutrients find their way into plants and other food, including larval mayflies and other insects for which the dipper dives.
“They’re truly fertilizing the river and so that makes its way all the way up through the food chain,” Tonra said….
Christopher M. Tonra, Kimberly Sager-Fradkin, Sarah A. Morley, Jeffrey J. Duda, Peter P. Marra. The rapid return of marine-derived nutrients to a freshwater food web following dam removal. Biological Conservation, 2015; 192: 130 DOI: 10.1016/j.biocon.2015.09.009